Derived gravity field of the seismogenic upper crust of SE Germany and West Bohemia and its comparison with seismicity

Abstract

The gravity field of the seismogenic upper crust was derived from the Bouguer gravity map by applying the Butterworth high-pass filter in the wave-number domain. The cutoff wavelength of the filter was 110 km, to pass the gravity signals of structures within the 18 km thick seismogenic layer. The derived residual gravity map reveals potential stress concentrating structures, which may cause seismicity provided they lie within the existing zones of weakness. Furthermore we derived a shaded relief map of the horizontal gravity gradient, which highlighted the tectonic lines accompanied by density contrast. The directional analysis of this map shows three dominant strike directions. The most prominent one is "the Hercynian" NW-SE strike direction represented by the Franconian Line, the Gera-Jáchymov Fault Zone and the Elbe Zone. The second dominant strike is the Rhenisch NNE-SSW trending represented by the Upper Rhine Graben Zone, RheinsbergHeldburg Line and several Proterozoic volcanic belts in the Teplá-Barrandien Unit. The third pronounced trending of the ENE-WSW direction is represented by the Erzgebirge and Eger Graben gravity low. The N-S trending Rostock-Leipzig-Regensburg Zone (Pritzwalk-Naab Lineament) is not distinctly reflected in the derived gravity maps, although many fault segments have a meridian direction.The relative reactivation potential of some pre-existing fault systems identified in the gravity map was studied with respect to the wide range of the recent stress configuration determined in the West Bohemia/Vogtland region. The resulting diagrams show that the steep NNW-SSE to N-S faults (represented by some segments of the Mariánské Lázně Fault Zone) are oriented favourably for reactivation. On the contrary, the orientation of the ENE-WSW faults limiting the Eger Graben (Litoměřice Fault, etc.) is unfavourable for reactivation for all dip values.

Pre-Late Carboniferous geology along the contact of the Saxothuringian and Teplá-Barrandian zones in the area covered by younger sediments and volcanics (western Bohemian Massif, Czech Republic)

“…At the same time, geophysical and geological observations in the Eger Graben area led to a formal definition of the surface demonstration of the Saxothuringian/Teplá-Barrandian boundary, which was then designated as the "Litoměřice deep fault" (Šťovíčková 1973). Gravimetric survey along this fault zone has revealed a chain of positive gravity anomalies and a steep gravity gradient towards the northwest indicating the boundary between low-density rocks of the Saxothuringian Zone and high-density rocks of the Teplá-Barrandian Zone (Šťovíčková 1973;Blížkovský et al 1994;Švancara et al 2008;Sedlák et al 2009). Seismic survey in the area of the Saxothuringian/Teplá-Barrandian boundary by Plomerová et al (2007) and has shown differences in orientation of the mantle fabric in these large-scale zones and led to delimitation of their contact in the mantle lithosphere.…”

Geomorphological evidence of tectonic activity of the Marianske Lazne Fault (Czech Republic) and its influence to stream network evolution

“…It is proposed that segments a, b, c, f, g and i were the more active ones in recent history (Pleistocene -Holocene?). Unfortunately, only segments a and b have been previously studied by palaeoseismology or detailed geophysics so far (Procházková et al, 1998;Švancara et al, 2008;Fischer et al, 2012;Halpaap et al, 2017;Blecha et al, 2018;Štěpančíková et al, 2019). These studies agree on that the youngest tectonic activity occurred in this NW part of the MLF.…”

“…However, the character of the fault escarpment varies in different parts of the MLF, it is possible to observe different grades of tectonic facets evolution, water stream erosion etc. This can indicate a complicated tectonic history and possibly the difference in age and rate of the tectonic movements in the particular segments of the MLF (Badura et al, 2007;Švancara et al, 2008). The MLF separates two distinct types of relief (Fischer et al, 2012): higher terrain on the eastern side and lower on the western.…”

“…1). The fault was reactivated several times during the Cenozoic, the last reactivation is of Neogene age and persists to this day (Švancara et al, 2008;Fischer et al, 2012). It controls significant effects in the terrain morphology such as a mountain front fault scarp that is up to 300 m high.…”